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Iodine

Other Name(s):

General description

In 1922, researchers discovered that the thyroid gland needs iodine to produce thyroid hormones and prevent the development of a goiter (enlarged thyroid glands). Thyroid hormones regulate metabolism and affect reproductive processes, nerves, muscles, skin, and hair. In addition to preventing goiters, iodine helps with the synthesis of protein and utilization of oxygen.

Iodine is incorporated into two important hormones produced by the thyroid gland. Together, these two hormones regulate the metabolic rate of the body. They are extremely important in growth and development, particularly in the fetus and newborn. Deficiencies of iodine and thyroid hormones can result in intellectual disability and developmental delays.

Medically valid uses

Goiters can be prevented by the use of table salt that has been fortified with potassium iodide. Other sources of iodine include eggs, dairy products, and seaweed. Appropriate treatment of goiter during pregnancy is particularly critical for the health of the fetus.

Unsubstantiated claims

Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.

Iodine has been said to reduce the risk of breast cancer, decrease fatigue, and prevent weight gain, as well as be useful in the treatment of arteriosclerosis (hardening of the arteries).

Recommended intake

Iodine supplements are essential for people living in the "goiter belt" (the Great Lakes states) or any other area lacking iodine in the soil. Adults who receive insufficient iodine in their diet can develop goiters (enlarged thyroid glands). If the lack of iodine is severe, they may also develop hypothyroidism (underactive thyroid gland). Memory difficulties and other cognitive problems can arise in adults who develop hypothyroidism.

It is estimated that before table salt was routinely supplemented with iodine, 50 to 70 percent of the people living in the Lake Michigan area had goiters. People who consume large amounts of "goitrogenic" vegetables such as cabbage, kale, Brussels sprouts, and rutabagas need additional iodine. Goitrogenic substances inhibit the absorption of iodine from the intestinal tract. Cooking deactivates goitrogenic substances.

Cretinism is a condition in which the thyroid gland did not function while the fetus was developing. This condition can lead to intellectual disability and inhibit physical growth.

As indicated below, iodine is measured in micrograms. The RDA is the Recommended Dietary Allowance.

Group

RDA

Infant (0 to 6 months)

40 mcg

Infant (6 months to 1 year)

50 mcg

Children (1 to 3 years)

70 mcg

Children (4 to 6 years)

90 mcg

Children (7 to 10 years)

120 mcg

Men (11+ years)

150 mcg

Women (11+ years)

150 mcg

Pregnant women

175 mcg

Breastfeeding women

200 mcg

Food source

Nutrient content per 100 grams

Seaweed

61,990 mcg*

Iodized salt

10,000 mcg

Cod liver oil

838 mcg

Seafood, fish (depending on type of fish)

36–311 mcg

Seafood, shellfish (depending on type of shellfish)

31–129 mcg

Sea salt

94 mcg

* mcg = micrograms

Newborn infants who had insufficient iodine available while developing in the uterus are typically born with enlarged thyroids and evidence of hypothyroidism. Severe hypothyroidism can result in growth abnormalities and profound intellectual disability.

Deficiencies in adults may result in a goiter. An insufficient intake of iodine may result in hypothyroidism. Signs of hypothyroidism include dry skin and hair, loss of physical and mental vigor and alertness, and weight gain.

Side effects, toxicity, and interactions

Elemental iodine, such as that found in "tincture of iodine" used to disinfect cuts, is extremely poisonous. Ingestion of even small amounts can be fatal.

Ingestion of potassium iodide or organically bound iodine preparations over a period of time, with doses approaching 1,000 micrograms/day can produce goiter and suppress the function of the thyroid. An excessive intake of iodine may cause a goiter similar to that seen with iodine deficiency. Excessive iodine also depresses the function of the thyroid, eventually causing a mild hypothyroidism.

Women who are pregnant or breastfeeding should not take iodine supplements without consulting a physician. Excessive iodine intake may produce hypothyroidism in the newborn and the appearance of a goiter.

Since iodine interacts with lithium carbonate (taken for the manic phase of manic depressive syndromes), those taking lithium should avoid taking iodine supplements. Using iodine and lithium together may result in hypothyroidism. Also, avoid taking iodine supplements at the same time as taking amiodarone (a drug to control heart arrhythmias).

Additional information

Many areas of the country contain very little iodine in the soil. Subsequently, crops produced in these areas and animals raised on these crops are exposed to very little iodine. Prior to the addition of iodine to table salt, these iodine-poor areas produced a large number of people with goiters (an enlargement of the thyroid gland caused by insufficient iodine in the diet). This problem has largely disappeared following the iodination of salt and the widespread consumption (even inland) of ocean fish and shellfish. However, despite iodized salt, daily iodine intake appears to be decreasing.

Iodized salt contains potassium iodide, usually in a ratio of one part iodine to 10,000–100,000 parts salt. Although this means there is actually very little iodine in salt, there is a sufficient amount to prevent the development of a goiter. Typically, iodized salt produced in the United States contains 76–100 micrograms of iodine per gram of salt.

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